Lakeland, FL -- 41-year-old Coach James Shannon Arnett is married and a father of four. And on Wednesday, he was arrested during football practice at Lake Gibson High School, charged with two felony counts of possessing child pornography.

"We know of at least two children that we are going to talk to, to see if there was any inappropriate contact with them," said Polk County Sheriff Grady Judd, "but we certainly fear that there may be other victims out there."

Sheriff Judd says Arnett recently reported losing a computer thumb drive at school. A student apparently found it, opened it up at home to see who it belonged to, and found thousands of images stored on it.

They included naked adult women, high school-aged girls and younger children with clothing on, but in in erotic poses. Two of the thousands of images, says Judd, rise to the level of illegal child pornography.

The student who found it turned it in.

"He went to the school resource deputy this week and said, 'I have a 12-year-old sister and I'm really PO'd by what I saw on this,'" said Judd.

Also disturbing: investigators say there are "a lot" of pictures of female students at Lake Gibson High School. They describe the girls as being in suggestive poses, such as leaning over desks.

Their images were in almost all cases, apparently snapped without their knowledge, says Judd.

Emily Thompson, a 9th grader, says it's creepy.

"It's definitely not funny," she said, "it's just... repulsing."

Several students say Arnett is a well-regarded coach and teacher. News of his arrest -- the talk of the campus today -- was a shocker.

"I really don't know what to believe. Coach Arnett seemed like a really good guy, and what happened was just terrible," said sophomore Aaron Stewart.

Investigators say Arnett also took similar pictures at a nearby park along Duff Road.

He's confessed to all of it, they say, except the child porn pics. He denies knowing anything about them. The sheriff says Arnett claimed he was introduced to porn at the age of 9, and has been addicted to it since then.

While the rest of the images may not be illegal, they are alarming, said Judd, and he questions whether Arnett had acted inappropriately in the past, or was possibly "grooming" children for something more sinister.

"Because we know that is a pattern of activity that follows this kind of photo taking," said Sheriff Judd.

Judd says there is no evidence Arnett ever abused any of his own four children.

Polk County School Board says Arnett, who has worked on-and-off 13 years with the district, has been placed on paid administrative leave pending the outcome of the investigation.

They've launched an internal investigation of their own, and plan to have crisis counselors on hand at Lake Gibson High School Friday to address any students' concerns.